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Sustainable Energy Science and Engineering CenterHydrogen ProductionSustainable Energy Science and Engineering CenterHydrogen ProductionSource:Sustainable Energy Science and Engineering CenterFeedstocks Usage in Hydrogen ProductionSource: NAS Study, 2004Sustainable Energy Science and Engineering CenterSustainable Paths to HydrogenSource:Sustainable Energy Science and Engineering CenterHydrogen Production MethodsMost methods of producing hydrogen involve splitting water (H2O) into its component parts of hydrogen (H2) and oxygen (O). The most common method involves steam reforming of methane (from natural gas), although there are several other methods.• Steam reforming converts methane (and other hydrocarbons in natural gas) into hydrogen and carbon monoxide by reaction with steam over a nickel catalyst• Electrolysis uses electrical current to split water into hydrogen at the cathode (+) and oxygen at the anode (-)• Steam electrolysis (a variation on conventional electrolysis) uses heat, instead of electricity, to provide some of the energy needed to split water, making the process more energy efficient• Thermochemical water splitting uses chemicals and heat in multiple steps to split water into its component parts• Photoelectrochemical systems use semi-conducting materials (like photovoltaics) to split water using only sunlight• Photobiological systems use microorganisms to split water using sunlight• Biological systems use microbes to break down a variety of biomass feed stocks into hydrogen• Thermal water splitting uses a very high temperature (approximately 1000°C) to split water• Gasification uses heat to break down biomass or coal into a gas from which pure hydrogen can be generatedSustainable Energy Science and Engineering CenterChemical Hydrogen ProductionSustainable Energy Science and Engineering CenterElectrolysisSustainable Energy Science and Engineering CenterElectrolysisSustainable Energy Science and Engineering CenterElectrolysis of WaterBy providing energy from a battery, water (H2O) can be dissociated into the diatomic molecules of hydrogen (H2) and oxygen (O2). This process is a good example of the the application of the four thermodynamic potentials (internal energy, U, Helmoltz free energy, F = U-TS; Enthalpy, H = U+pv and Gibbs free energy, G =U+pv-TS.The electrolysis of one mole of water produces a mole of hydrogen gas and a half a mole of oxygen gas in their normal diatomic forms. A detailed analysis of this process makes use of the thermodynamic potentials and the first law of thermodynamics. This process is presumed to be at 298K and atmospheric pressure.Sustainable Energy Science and Engineering CenterQuanitity H2OH20.5O2ChangeEnthalpy -285.83kJ 0 0 ∆H = -285.83kJEntropy 69.91 J/K 130.68J/K 0.5x205.14J/K T∆S = 48.7 kJSystem work: W = P∆V = (101.3 kPa)(1.5 moles)(22.4x10-3m3/mol)(298K/273K) = 3715 J ∆U = ∆H-P ∆V = 285.83kJ-3.72 kJ = 282.1 kJ ∆G = ∆H-T ∆S = 285.83 kJ-48.7 kJ = 237.1 kJElectrolysis of WaterSustainable Energy Science and Engineering CenterEfficiencySystems that claim 85 % Improved electrolysis efficiency can bring the PV-hydrogen efficiency to about 10%Sustainable Energy Science and Engineering CenterWATER AVAILABILITYThere is enough water to sustain hydrogen!Sustainable Energy Science and Engineering CenterHydrogen-ElectricitySustainable Energy Science and Engineering CenterElectrolyzersSustainable Energy Science and Engineering CenterLarge scale ElectrolyzersSustainable Energy Science and Engineering CenterLOW CURRENT ELECTROLYSIS OF WATER by Ph. M. KanarevThe most modern Electrolyzers consume 4.0 kWh per cubic meter of H2gas. Electrolysis process takes place by voltage of 1.6-2.0 V and current strength of dozens and hundreds of amperes. When one cubic meter of hydrogen is burnt, 3.55 kWh of energy is released [1].A money-saving process of decomposition of water molecules into hydrogen and oxygen exists in the nature. This process takes place during photosynthesis. Hydrogen atoms are separated from water molecules and are used as connecting links while forming organic molecules, and oxygen is released into the air.A question emerges: is it possible to model an electrolytical process of water decomposition into hydrogen and oxygen, which takes place during photosynthesis? A search of a reply to this question has resulted in a simple structure of a cell (Fig. 1), in which the process takes place by voltage of 1.5-2.0 V between the anode and the cathode and amperage of 0.02 amperes [1], [2]. http://guns.connect.fi/innoplaza/energy/story/Kanarev/electrolysis/Low Current Electrolysis of WaterSustainable Energy Science and Engineering CenterThe electrodes of the cell are made of steel. It helps to avoid the phenomena, which are appropriate to a galvanic cell. Nevertheless, at the cell electrodes a potential difference of nearly 0.1 V takes place in complete default of electrolytic solution in it. When the solution is charged, the potential difference is increased. The positive sign of the charge appears on the upper electrode always, and the negative sign appears on the lower one. If a direct current source generates pulses, gas output is increased.As a laboratory model of the low current electrolyzer cell generates small quantity of gases, a solution mass change definition method during the experiment and further calculation of released hydrogen and oxygen is the most reliable method of definition of their quantity. It is known that a gram atom is equal to atomic mass of substance; a gram molecule is equal to molecular mass of substance. For example, the gram molecule of hydrogen in the water molecule is equal to two grams; the gram-atom of the oxygen atom is 16 grams. The gram molecule of water is equal to 18 grams. Hydrogen mass in a water molecule is 2x100/18=11.11%; oxygen mass is 16x100/18=88.89%; this ratio of hydrogen and oxygen is in one liter of water. It means that 111.11 grams of hydrogen and 888.89 grams of oxygen are in 1000 grams of water.One liter of hydrogen weighs 0.09 g; one liter of oxygen weighs 1.47 g. It means that it is possible to produce 111.11/0.09=1234.44 liters of hydrogen and 888.89/1.47=604.69 liters of oxygen from one liter of water. It appears from this that one gram of water contains 1.23 liters of hydrogen. Energy consumption for production of 1000 liters of hydrogen is 4 kWh and for one liter 4 Wh. As it is possible to produce 1.234 liters of hydrogen from one gram of


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FSU EML 4930r - Lecture Notes

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